1. Field of the Invention:
This invention relates to electric lamps and has particular reference to an improved filament-support means for tubular incandescent lamps that have elongated coiled filaments. 2. Description of the Prior Art:
Incandescent lamps having helically-coiled filaments that are held in suspended position within a tubular envelope by various kinds of support members are generally well known in the art.
A tubular lamp of this type having a filament-support member made from wire that is bent to form two circular loops which engage the arcuate side walls of the envelope and are joined by a medial segment that includes a scissors-like clamp that is coupled to a secondary turn of the coiled-coil filament is disclosed in U.S. Pat. No. 3,173,051, granted Mar. 9, 1965 to Berlinghof et al. One of the loops may be provided with a crimp or fold that engages the exhaust tip cavity and thus retains the wire support in place within the envelope (FIG. 3 embodiment).
Single-ended and double-ended incandescent lamps having tubular envelopes with a U-shaped wire support that has both of its legs anchored in the envelope seal and its bent end formed into a loop that encircles the coiled filament is disclosed in U.S. Pat. No. 3,270,238, issued Aug. 30, 1966 to Mosby. A filament-support member for a tubular incandescent lamp formed from a straight piece of wire that extends along the inner surface of the envelope, has both ends embedded in the press seals formed at each end of the envelope and which includes a centrally-located loop or hook that is coupled to a secondary turn of the coiled-coil filament is disclosed in U.S. Pat. No. 3,335,312, granted Aug. 8, 1967 to Cardwell, Jr. A similar support member for a coiled-coil filament is disclosed in U.S. Pat. No. 3,390,299 (issued June 25, 1968 to VanSickler et al.) and consists of a wire member having one leg that is anchored in the sealed end of the envelope and is terminated by a loop which is coupled to one of the secondary turns of the filament and has an upstanding leg segment that protrudes into sealed residue of the exhaust tube portion of the envelope. In the FIGS. 8 and 9 embodiments, the upstanding leg segments are formed by retroverted medial segments of the support wires and the coupling-loops are located at the free ends of the respective supports.
In accordance with a more recent proposal, one end of the support wire for the coiled-coil filament of a tubular type lamp is anchored in one of the envelope seals and has a medial segment which is bent into a triangular-shaped loop that loosely encircles the filament barrel and engages the inner surface of the envelope. A support member of this construction is shown in U.S. Pat. No. 3,521,112 (issued July 21, 1970 to Walsh et al.). The patentees also disclose an alternative lamp embodiment (FIG. 7) which employs a wire support member that has a pair of overlapping leg segments and is terminated by a spiral which loosely encircles the barrel portion of the coiled-coil filament and also engages the inner wall of the tubular envelope in such a manner that the axially-extending leg segments of the support are seated against the opposite wall of the envelope, thus eliminating the need for anchoring one or both legs in the envelope seals.
Tubular incandescent lamps having filament-support wires with helically-coiled portions of large and small diameter that engage the envelope walls and the barrel portion of the coiled-coil filament, respectively, are disclosed in U.S. Pat. Nos. 3,736,455 (granted May 29, 1973 to Notelteirs et al.) and 3,784,865 (granted Jan. 8, 1974 to Shanks).